remove cancellation points in stdio

commit 58165923890865a6ac042fafce13f440ee986fd9 added these optional
cancellation points on the basis that cancellable stdio could be
useful, to unblock threads stuck on stdio operations that will never
complete. however, the only way to ensure that cancellation can
achieve this is to violate the rules for side effects when
cancellation is acted upon, discarding knowledge of any partial data
transfer already completed. our implementation exhibited this behavior
and was thus non-conforming.

in addition to improving correctness, removing these cancellation
points moderately reduces code size, and should significantly improve
performance on i386, where sysenter/syscall instructions can be used
instead of "int $128" for non-cancellable syscalls.

diff --git a/src/stdio/__stdio_read.c b/src/stdio/__stdio_read.c
index 5947344..f8fa6d3 100644 (file)
--- a/src/stdio/__stdio_read.c
+++ b/src/stdio/__stdio_read.c
@@ -1,12 +1,5 @@
 #include "stdio_impl.h"
 #include <sys/uio.h>
-#include <pthread.h>
-
-static void cleanup(void *p)
-{
-       FILE *f = p;
-       if (!f->lockcount) __unlockfile(f);
-}
 
 size_t __stdio_read(FILE *f, unsigned char *buf, size_t len)
 {
@@ -16,9 +9,7 @@ size_t __stdio_read(FILE *f, unsigned char *buf, size_t len)
        };
        ssize_t cnt;
 
-       pthread_cleanup_push(cleanup, f);
-       cnt = syscall_cp(SYS_readv, f->fd, iov, 2);
-       pthread_cleanup_pop(0);
+       cnt = syscall(SYS_readv, f->fd, iov, 2);
        if (cnt <= 0) {
                f->flags |= F_EOF ^ ((F_ERR^F_EOF) & cnt);
                return cnt;

diff --git a/src/stdio/__stdio_write.c b/src/stdio/__stdio_write.c
index 8c89389..d2d8947 100644 (file)
--- a/src/stdio/__stdio_write.c
+++ b/src/stdio/__stdio_write.c
@@ -1,12 +1,5 @@
 #include "stdio_impl.h"
 #include <sys/uio.h>
-#include <pthread.h>
-
-static void cleanup(void *p)
-{
-       FILE *f = p;
-       if (!f->lockcount) __unlockfile(f);
-}
 
 size_t __stdio_write(FILE *f, const unsigned char *buf, size_t len)
 {
@@ -19,9 +12,7 @@ size_t __stdio_write(FILE *f, const unsigned char *buf, size_t len)
        int iovcnt = 2;
        ssize_t cnt;
        for (;;) {
-               pthread_cleanup_push(cleanup, f);
-               cnt = syscall_cp(SYS_writev, f->fd, iov, iovcnt);
-               pthread_cleanup_pop(0);
+               cnt = syscall(SYS_writev, f->fd, iov, iovcnt);
                if (cnt == rem) {
                        f->wend = f->buf + f->buf_size;
                        f->wpos = f->wbase = f->buf;
@@ -34,11 +25,8 @@ size_t __stdio_write(FILE *f, const unsigned char *buf, size_t len)
                }
                rem -= cnt;
                if (cnt > iov[0].iov_len) {
-                       f->wpos = f->wbase = f->buf;
                        cnt -= iov[0].iov_len;
                        iov++; iovcnt--;
-               } else if (iovcnt == 2) {
-                       f->wbase += cnt;
                }
                iov[0].iov_base = (char *)iov[0].iov_base + cnt;
                iov[0].iov_len -= cnt;

diff --git a/src/stdio/fopen.c b/src/stdio/fopen.c
index 07bdb6e..252f082 100644 (file)
--- a/src/stdio/fopen.c
+++ b/src/stdio/fopen.c
@@ -18,7 +18,7 @@ FILE *fopen(const char *restrict filename, const char *restrict mode)
        /* Compute the flags to pass to open() */
        flags = __fmodeflags(mode);
 
-       fd = sys_open_cp(filename, flags, 0666);
+       fd = sys_open(filename, flags, 0666);
        if (fd < 0) return 0;
        if (flags & O_CLOEXEC)
                __syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);